The disclosure relates generally to power generation systems, and more particularly, to a power generation system including a gas turbine system having a compressor creating an excess air flow and a turbo-expander to augment generator output and increase turbine exhaust gas mass flow of another gas turbine system, which turbine exhaust(s) may be used in one or more steam generators.
Power generation systems oftentimes employ one or more gas turbine systems, which may be coupled with one or more steam turbine systems, to generate power. A gas turbine system may include a multi-stage axial flow compressor having a rotating shaft. Air enters the inlet of the compressor and is compressed by the compressor blade stages and then is discharged to a combustor where fuel, such as natural gas, is burned to provide a high energy combustion gas flow to drive a turbine component. In the turbine component, the energy of the hot gases is converted into work, some of which may be used to drive the integral compressor through a rotating shaft, with the remainder available for useful work to drive a load such as a generator via a rotating shaft (e.g., an extension of the rotating shaft) for producing electricity. A number of gas turbine systems may be employed in parallel within a power generation system. In a combined cycle system, one or more steam turbine systems may also be employed with the gas turbine system(s). In this setting, a hot exhaust gas from the gas turbine system(s) is fed to one or more heat recovery steam generators (HRSG) to create steam, which is then fed to a steam turbine component having a separate or integral rotating shaft with the gas turbine system(s). In any event, the energy of the steam is converted into work, which can be employed to drive a load such as a generator for producing electricity.
When a power generation system is created, its parts are configured to work together to provide a system having a desired power output. The ability to increase power output on demand and/or maintain power output under challenging environmental settings is a continuous challenge in the industry. For example, on hot days, the electric consumption is increased, thus increasing power generation demand. Another challenge of hot days is that as temperature increases, compressor flow decreases, which results in decreased generator output. One approach to increase power output (or maintain power output, e.g., on hot days) is to add components to the power generation system that can increase air flow to the combustor of the gas turbine system(s). One approach to increase air flow is adding a storage vessel to feed the gas turbine combustor. This particular approach, however, typically requires a separate power source for the storage vessel, which is not efficient.
Another approach to increasing air flow is to upgrade the compressor. Currently, compressors have been improved such that their flow capacity is higher than their predecessor compressors. These new, higher capacity compressors are typically manufactured to either accommodate new, similarly configured combustors, or older combustors capable of handling the increased capacity. A challenge to upgrading older gas turbine systems to employ the newer, higher capacity compressors is that there is currently no mechanism to employ the higher capacity compressors with systems that cannot handle the increased capacity without upgrading other expensive parts of the system. Other parts that oftentimes need to be upgraded simultaneously with a compressor upgrade include but are not limited to the combustor, gas turbine component, generator, transformer, switchgear, HRSG, steam turbine component, steam turbine control valves, etc. Consequently, even though a compressor upgrade may be theoretically advisable, the added costs of upgrading other parts renders the upgrade ill-advised due to the additional expense.